This invention relates, in general, to motion producing apparatus and, more particularly, to actuators of the electromagnetic kind.
A wide variety of such actuators exist. Typically, electromagnetic motors or actuators include a cylindrical bobbin about which is wound one or more field coils. Mounted within the bobbin is an armature which may be comprised of a core formed from a piece of soft iron, as shown in U.S. Pat. No. 3,728,654, or it may be comprised of a plurality of permanent magnets, such as shown in U.S. Pat. Nos. 3,022,400, 3,202,886 and 3,495,147, or the armature may be a combination of a core and a permanent magnet. Through the application of direct current in one direction to the field coil, a magnetic field is generated for producing a force sufficient for driving the armature in a given direction. Reverse application of the direct current to the field coil causes the armature to be driven in the opposite direction.
In commonly assigned and copending application Ser. No. 45,822, entitled "Linear Motor", filed June 5, 1979, by the applicant of the instant invention, there is disclosed an improved actuator which automatically returns a movable armature to an original position upon deenergization. In commonly assigned U.S. Pat. No. 4,265,530, entitled "Shutter Blade Drive System", issued May 5, 1981, by the applicant of the instant application, there is disclosed a photographic apparatus employing a linear motor for controlling the indexing of a shutter mechanism. Besides the linear motor, use is also made of an electromagnetic coupling device which is energized when the motor is energized. The coupling device serves, upon energization, to interconnect the motor armature to the shutter mechanism. Deenergization of both motor and coupling device allow the armature to return to its original position. Thus, for every incremental advance of the shutter the armature and coupling device travel a single stroke and then must return to their original positions for another stroke to incrementally advance the shutter. In commonly assigned U.S. Pat. No. 4,264,154, entitled "Apparatus for Automatically Controlling Transmission of Light Through a Lens System", issued April 28, 1981, by the applicant of the instant invention, there is disclosed a linear motor and coupling device similar to the last-noted type which indexes a polarized lens element.
The foregoing actuators are extremely effective and are also miniature. They can be used in a variety of situations where space, weight and low electric power consumption are desired. Despite their many advantages, however, there are certain drawbacks connected with their use. One is the fact that each armature itself cannot be incrementally advanced to a plurality of linear positions. Because of this, each of such actuators must operate with an additional electromagnetic coupling device to achieve incremental advance of the output member. Moreover, because such actuators rely on mechanical stops precise positioning of the output member is a potential problem.
Commonly assigned U.S. Pat. No. 3,882,522, issued May 6, 1972, discloses use of a rotary stepping motor for supplying motive power to shutter blades. A shortcoming of rotary actuators is that they require mechanical converters for converting rotor motion to a linear driving output motion. Stated otherwise, they cannot directly linearly drive an output member. Thus, there is a possibility that the rotor can be driven, by its own momentum, beyond any desired position.